James Fadiman is an American writer known for his research on microdosing psychedelics. He and Robert Frager co-founded the Institute of Transpersonal Psychology, which later became Sofia University, where he was a lecturer in psychedelic studies.

Fadiman received a Bachelor of Arts degree from Harvard University in 1960 and a Master's degree and a doctorate (both in psychology) from Stanford University, the PhD in 1965. While in Paris in 1961, his friend and former Harvard undergraduate adviser, Ram Dass (then known as Richard Alpert), introduced him to psilocybin. As a graduate student at Stanford, Fadiman was Stewart Brand's LSD guide on Brand's first LSD trip in 1962, at Myron Stolaroff's International Foundation for Advanced Study in Menlo Park, California. While living in Menlo Park, Fadiman and his wife were Ken Kesey's Perry Lane neighbors and friends.

In the early sixties Fadiman was also part of the team in the psychedelics in problem-solving experiment at the International Foundation for Advanced Study, which was abruptly halted in 1966.^[

Fadiman’s 2011 book The Psychedelic Explorer’s Guide discussed the use of psychedelics in sub perceptual doses and unknowingly helped to drive the modern microdosing movement. Fadiman is a proponent of microdosing. He writes and lectures on the topic and collects anecdotal reports from those who practice it.